1. Technical Field
The present invention relates to a technology for allowing a user to receive contents such as music, video, and programs via a network, within the limits of a prepaid amount of money, and use the received contents.
2. Background Art
The recent prevalence of broadband networks such as ADSL allows users to receive contents such as music, video, and programs from content distributors via a network, within the limits of a prepaid amount of money, and use the received contents. In general, the contents are distributed in an encrypted form to protect them from problems such as copyright infringement, and the users decrypt the received encrypted contents to use the contents.
When a user purchases content via a network, the user needs to pay a fee for the content. in one method for the payment, the user may transfer the money using Public Key Infrastructure (PKI) such as Secure Sockets Layer (SSL) in which the bank account number or credit card number of the user is used for identification. In another method, the user may be charged later from the content distributor who manages use fees for users.
With the former method, there is a fear that a third party may obtain the bank account number or the credit card number by an unauthorized means such as eaves dropping. With the latter method, a system for managing the use fees and charging the users needs to be established, which would make the system of the content distributor complicated.
Japanese Laid-Open Patent Application No. 2001-60286 discloses a prepaid recording medium that provides a payment method which is easier than conventional ones. The prepaid recording medium is a non-volatile semiconductor memory card or a card-type recording medium such as an optical disc or a magnetic recording disk, and is of a type in which data can be written. The prepaid recording medium has a prepaid information storage area for storing accounting data that indicates amounts of money prepaid for contents distributed from a distribution center, a content information storage area for storing various pieces of information of the contents distributed from the distribution center, and an area for storing decryption keys used for decrypting encrypted contents. The construction enables encrypted contents corresponding to the decryption keys to be downloaded or copied within the limits of prepaid amounts of money.
In general, each content is assigned with a different pair of an encryption key, which is used to encrypt the content to generate an encrypted content, and a decryption key which is used to decrypt the encrypted content.
The above-described prepaid recording medium enables only such encrypted contents that can be decrypted using the corresponding decryption keys, to be downloaded or copied. As a result, when a user purchases such a prepaid recording medium, the user needs to determine, in advance, contents that the user would like to use by downloading or copying them from the content distributor. That is to say, the contents the user can use depend on the decryption keys stored in the prepaid recording medium.
The above-described conventional technology, however, does not make full use of the advantageous effect of the prepaid card so that the user can purchase any desired contents within the limits of a prepaid amount of money.